The ngx_stream_upstream_module module (1.9.0) is used to define groups of servers that can be referenced by the  directive.

upstream backend {    hash $remote_addr consistent;    server backend1.example.com:12345  weight=5;    server backend2.example.com:12345;    server unix:/tmp/backend3;    server backup1.example.com:12345   backup;    server backup2.example.com:12345   backup;}server {    listen 12346;    proxy_pass backend;}

Dynamically configurable group with periodic  is available as part of our :

resolver 10.0.0.1;upstream dynamic {    zone upstream_dynamic 64k;    server backend1.example.com:12345 weight=5;    server backend2.example.com:12345 fail_timeout=5s slow_start=30s;    server 192.0.2.1:12345            max_fails=3;    server backend3.example.com:12345 resolve;    server backend4.example.com       service=http resolve;    server backup1.example.com:12345  backup;    server backup2.example.com:12345  backup;}server {    listen 12346;    proxy_pass dynamic;    health_check;}

Defines a group of servers. Servers can listen on different ports. In addition, servers listening on TCP and UNIX-domain sockets can be mixed.

Example:

upstream backend {    server backend1.example.com:12345 weight=5;    server 127.0.0.1:12345            max_fails=3 fail_timeout=30s;    server unix:/tmp/backend2;    server backend3.example.com:12345 resolve;    server backup1.example.com:12345  backup;}

By default, connections are distributed between the servers using a weighted round-robin balancing method. In the above example, each 7 connections will be distributed as follows: 5 connections go to backend1.example.com:12345 and one connection to each of the second and third servers. If an error occurs during communication with a server, the connection will be passed to the next server, and so on until all of the functioning servers will be tried. If communication with all servers fails, the connection will be closed.

Defines the address and other parameters of a server. The address can be specified as a domain name or IP address with an obligatory port, or as a UNIX-domain socket path specified after the “unix:” prefix. A domain name that resolves to several IP addresses defines multiple servers at once.

The following parameters can be defined:

weight=

number

sets the weight of the server, by default, 1.

max_conns=

number

limits the maximum 

number of simultaneous connections to the proxied server (1.11.5). Default value is zero, meaning there is no limit. If the server group does not reside in the  , the limitation works per each worker process.

Prior to version 1.11.5, this parameter was available as part of our  .

max_fails=

number

sets the number of unsuccessful attempts to communicate with the server that should happen in the duration set by the 

fail_timeout parameter to consider the server unavailable for a duration also set by the 

fail_timeout parameter. By default, the number of unsuccessful attempts is set to 1. The zero value disables the accounting of attempts. Here, an unsuccessful attempt is an error or timeout while establishing a connection with the server.

fail_timeout=

time

sets

• the time during which the specified number of unsuccessful attempts to communicate with the server should happen to consider the server unavailable;
• and the period of time the server will be considered unavailable.

By default, the parameter is set to 10 seconds.

backup

marks the server as a backup server. Connections to the backup server will be passed when the primary servers are unavailable.

down

marks the server as permanently unavailable.

Additionally, the following parameters are available as part of our :

resolve

monitors changes of the IP addresses that correspond to a domain name of the server, and automatically modifies the upstream configuration without the need of restarting nginx. The server group must reside in the  .

In order for this parameter to work, the  directive must be specified in the block. Example:

stream {    resolver 10.0.0.1;    upstream u {        zone ...;        ...        server example.com:12345 resolve;    }}

 

service=

name

enables resolving of DNS   records and sets the service 

name (1.9.13). In order for this parameter to work, it is necessary to specify the   parameter for the server and specify a hostname without a port number.

If the service name does not contain a dot (“.”), then the -compliant name is constructed and the TCP protocol is added to the service prefix. For example, to look up the_http._tcp.backend.example.com SRV record, it is necessary to specify the directive:

server backend.example.com service=http resolve;

If the service name contains one or more dots, then the name is constructed by joining the service prefix and the server name. For example, to look up the _http._tcp.backend.example.com and server1.backend.example.com SRV records, it is necessary to specify the directives:

server backend.example.com service=_http._tcp resolve;server example.com service=server1.backend resolve;

 

Highest-priority SRV records (records with the same lowest-number priority value) are resolved as primary servers, the rest of SRV records are resolved as backup servers. If the parameter is specified for the server,  high-priority SRV records are resolved as backup servers, the rest of SRV records are ignored.

slow_start=

time

sets the 

time during which the server will recover its weight from zero to a nominal value, when unhealthy server becomes  , or when the server becomes available after a period of time it was considered  . Default value is zero, i.e. slow start is disabled.

The parameter cannot be used along with the   load balancing method.

If there is only a single server in a group, 

max_fails, 

fail_timeout and 

slow_start parameters are ignored, and such a server will never be considered unavailable.

Defines the name and size of the shared memory zone that keeps the group’s configuration and run-time state that are shared between worker processes. Several groups may share the same zone. In this case, it is enough to specify the zone size only once.

Additionally, as part of our , such groups allow changing the group membership or modifying the settings of a particular server without the need of restarting nginx. The configuration is accessible via the  module (1.13.3).

Prior to version 1.13.3, the configuration was accessible only via a special location handled by  .

Specifies a file that keeps the state of the dynamically configurable group.

Examples:

state /var/lib/nginx/state/servers.conf; # path for Linuxstate /var/db/nginx/state/servers.conf;  # path for FreeBSD

The state is currently limited to the list of servers with their parameters. The file is read when parsing the configuration and is updated each time the upstream configuration is . Changing the file content directly should be avoided. The directive cannot be used along with the  directive.

Changes made during   or   can be lost.

This directive is available as part of our  .

Specifies a load balancing method for a server group where client-server mapping is based on the hashed key value. The key can contain text, variables, and their combinations (1.11.2). Usage example:

hash $remote_addr;

Note that adding or removing a server from the group may result in remapping most of the keys to different servers. The method is compatible with the  Perl library.

If the consistent parameter is specified, the  consistent hashing method will be used instead. The method ensures that only a few keys will be remapped to different servers when a server is added to or removed from the group. This helps to achieve a higher cache hit ratio for caching servers. The method is compatible with the  Perl library with the ketama_points parameter set to 160.

Specifies that a server group should use a load balancing method where a connection is passed to the server with the least number of active connections, taking into account weights of servers. If there are several such servers, they are tried in turn using a weighted round-robin balancing method.

Specifies that a group should use a load balancing method where a connection is passed to the server with the least average time and least number of active connections, taking into account weights of servers. If there are several such servers, they are tried in turn using a weighted round-robin balancing method.

If the connect parameter is specified, time to connect to the upstream server is used. If the first_byte parameter is specified, time to receive the first byte of data is used. If the last_byteis specified, time to receive the last byte of data is used.  If the inflight parameter is specified (1.11.6), incomplete connections are also taken into account.

Prior to version 1.11.6, incomplete connections were taken into account by default.

This directive is available as part of our  .

The ngx_stream_upstream_module module supports the following embedded variables:

$upstream_addr

keeps the IP address and port, or the path to the UNIX-domain socket of the upstream server (1.11.4). If several servers were contacted during proxying, their addresses are separated by commas, e.g. “

192.168.1.1:12345, 192.168.1.2:12345, unix:/tmp/sock”. If a server cannot be selected, the variable keeps the name of the server group.

$upstream_bytes_sent

number of bytes sent to an upstream server (1.11.4). Values from several connections are separated by commas like addresses in the   variable.

$upstream_bytes_received

number of bytes received from an upstream server (1.11.4). Values from several connections are separated by commas like addresses in the   variable.

$upstream_connect_time

time to connect to the upstream server (1.11.4); the time is kept in seconds with millisecond resolution. Times of several connections are separated by commas like addresses in the  variable.

$upstream_first_byte_time

time to receive the first byte of data (1.11.4); the time is kept in seconds with millisecond resolution. Times of several connections are separated by commas like addresses in the  variable.

$upstream_session_time

session duration in seconds with millisecond resolution (1.11.4). Times of several connections are separated by commas like addresses in the   variable.